Minimizing the impact of approaching boats on nesting shorebirds

Juvenile black skimmers (Rynchops niger).If you ever walked along an empty stretch of beach and flushed away a flock of frightened shore birds, you might have wondered to yourself whether you just committed a horrible ecological sin.

Perhaps you asked yourself, "Where are those birds going? Did they just abandon their nestlings? How long until they come back? Or better yet, will they ever come back?"

A new study tries to answer these types of questions with respect to the impact of Black skimmer chick and egg in nest. So cute! Image credit, Donna Dewhurst.recreational boaters on nesting colonies of black skimmers in New Jersey where the birds are listed as endangered.  As it turns out, the answers can help coastal managers develop scientifically informed regulations such as setting no-entry buffer zones around nesting colonies to minimize human impact.

In the case of black skimmers, Joanna Burger from Rutgers and fellow researchers set up an experiment in which they approached nesting colonies by boat and measured a number of variables about the birds' response including how close the boat came before the birds flew away and how long it took for them to return. The results show that the shorebird's response to human disturbance depends on their reproductive stage.

During the pre-egg laying stage, the black skimmers, on average, would flush when boats came within 110 meters and would return, on average, 9.5 minutes later. However, after eggs were laid - during the incubation, hatching, and small chick phases - the flush distance decreased to 70-80 meters and the average time to return was around 1 minute.

The researchers hypothesize that during these post-egg laying phases, the birds are still stressed by the boats but are more reluctant to leave their nests unattended and their chicks at-risk to predation and heat stress.

Unfortunately, these are not the only potential negative impacts from boats on breeding shorebirds. Past studies on nesting common terns in the same area found that repeated disturbance by approaching boats eventually led to the birds abandoning their nesting habitat to move farther away from the ruckus.

Given these potential issues, the authors recommend that managers set a no-entry buffer zone, which is far enough back to ensure that the birds do not fly at any time from the colony edge. Based on this criteria and their study data, they recommended a minimum set back of 120 meters for black skimmers, which is greater than the 95% percentile of the distance that the birds first flew in response to approaching boats.

This method of measuring response distances to establish protective zones is likely applicable to any shore birds facing repeated disturbance from boats or other types of recreation.

--Reviewed by Rob Goldstein

Burger, J., Gochfeld, M., Jenkins, C., & Lesser, F. (2010). Effect of Approaching Boats on Nesting Black Skimmers: Using Response Distances to Establish Protective Buffer Zones Journal of Wildlife Management, 74 (1), 102-108 DOI: 10.2193/2008-576